The invention relates to a base for printing plates which consists of a particular aluminum alloy containing iron and manganese, and a printing plate containing such a base and at least one reproduction layer.
Radiation-sensitive or photosensitive reproduction layers are used, for example, in the production of offset printing plates and photoresists, i.e., they are generally applied onto a base by the user or by the industrial manufacturer. The bases employed in these copying materials are metals such as zinc, magnesium, chromium, copper, brass, steel, silicon, aluminum or combinations of these metals, plastic films, paper or similar materials. While these bases can be coated with the radiation-sensitive reproduction layer without being subjected to a modifying pretreatment, preferably they are coated after surface modification, such as by mechanical, chemical and/or electrochemical roughening, by oxidation and/or by treatment with hydrophilizing agents. Hydrophilizing agents are particularly used in the case of bases for offset printing plates constructed of aluminum or one of its alloys. The usual radiation-sensitive reproduction layers contain not only at least one radiation-sensitive compound, but in general also contain an organic binder, such as a resin, and if appropriate, plasticizers, pigments, dyes, wetting agents, sensitizers, adhesion promoters, indicators and other conventional additives. These reproduction layers are irradiated (i.e., exposed) and then developed in order to produce an image. A printing plate may, for example, be obtained in this manner.
The aluminum alloys described below are among the materials disclosed in the prior art for use in printing plates, the alloys mentioned in the first three references being commercial products available on the European, American and/or Japanese market.
__________________________________________________________________________ Alloy designation/ Composition of the alloy in % by weight of (remainder is Al) reference Si Cu Mn Mg Cr Zn Fe Ti Others __________________________________________________________________________ "1100" 0.375 0.05 -- -- -- -- 0.375 -- -- "3003" 0.2 0.05 0.7 -- -- 0.2 0.15 0.2 -- "A 19" 0.375 0.05 -- 0.9 -- -- 0.375 -- -- US-A 4 383 897 "Pure aluminum" 0.3 0.02 -- -- -- 0.07 0.4 0.03 0.03.sup.1 (DIN material 3.0255) "DIN material 3.0515" 0.5 0.1 0.8-1.5 0-0.3 -- 0.2 0.5 0.2 0.15.sup.2 EP-B 0 004 569 (= US-A 4 211 619) "1S" 0.25 -- -- -- -- -- -- -- -- "2S" 0.4 -- -- 0.6 -- -- -- -- -- "3S" -- -- 1.2 -- -- -- -- -- -- "24S" -- 4.5 0.6 1.5 -- -- -- -- -- "52S" -- -- -- 2.5 0.25 -- -- -- -- "61S" 0.6 0.25 -- 1.0 0.25 -- -- -- -- "75S" -- 1.60 -- 2.50 0.30 5.60 -- -- -- DE-A 29 12 060 (= US-A 4 301 229) DE-B 11 60 639 0.8-1.2 1.4-1.6 0.5-0.9 0.8-1.2 -- 0.1-0.3 0.5 -- -- DE-A 19 29 146 0.2-0.4 0.05-0.3 0.8-1.4 0.8-2.5 -- 0.01-0.2 0.2-0.6 0.01-0.05 0.001-0.005 B (= US-A 3 672 878 and 3 717 915 DE-A 25 37 819 0.5-1.5 0-0.5 0.005-0.4 0.4-1.2 0-0.3 0-0.5 0.05-0.5 0-0.05 0-0.005 B DE-A 32 32 810 0.05-0.30 up to -- 0.05-0.30 -- -- 0.15-0.30 up to up to (= US-A 4 435 230) 0.05 0.03 0.01 B EP-A 0 067 056 0.11-0.14 0.01- 0.004- 0.002- 0.01 0.01 0.33-1.31 0.01- --.sup.3 0.13 0.01 0.02 0.03 0.16-0.54 0.05- 0.02-1.02 0.03-1.15 0.01- 0.01 0.39-0.76 0.03- --.sup.4 0.15 0.02 0.16 EP-A 0 067 632 0.07-0.11 0.01 0.004- 0.002- 0.005- 0.01 0.15-0.29 0.01- --.sup.3 0.005 0.003 0.01 0.02 0.56 0.03 0.02 0.02 0.01 0.01 0.79 0.18 --.sup.4 EP-A 0 096 347.sup.5 -- 0 to 2 -- 0-0.6 -- 0-0.30 0.20-1.00 -- 0-0.05 Sn 0-0.06 In 0-0.03 Ga EP-A 0 097 318 0.02-0.15 up to up to 0.05 up to -- up to 0.1-1.0 up to -- 0.003 0.05 0.05 0.03 __________________________________________________________________________ .sup.1 maximum sum of the nonAl components: 0.5 .sup.2 maximum sum of the nonAl components: 1.5 .sup.3 as a singlelayer material or as a top layer .sup.4 as the core in a multilayer material .sup.5 Sn, In, Ga and/or Zn are present in amounts from 0.005 to 0.1
The particular advantages of each of the alloys and of the printing plate bases produced therefrom, are stated as being:
high stretchability coupled with permanent elongation after the stretching process, advantageous yield point relationship as a result of a low yield point and high strength, good dimensional stability of the printing plates during storage (German Auslegeschrift No. 1,160,639);
close fit when clamped on the printing cylinder; the clamped ends of the printing plates can readily be bent over (German Offenlegungsschrift No. 1,929,146);
improved resistance to fatigue, high tensile strength, good extensibility and high flexibility (German Offenlegungsschrift No. 2,537,819);
high resistance to fatigue coupled with a uniformly roughened surface (German Offenlegungsschrift No. 3,232,810) achieved by special production in the following stages: heat treatment at 450.degree. to 600.degree. C., hot-rolling, cold-rolling with reduction (deformation rate) of at least 70%, heating at 150.degree. to 250.degree. C. for at least 1 hour;
uniformly roughened surface, good mechanical properties during printing, even at high printing speeds, good dimensional stability even for relatively thin plates (European patent application No. 0,067,056) because the particle size of the intermetallic compounds is less than 3 .mu.m, these being present directly below the outer surface of the hot-rolled, cold-rolled, heated and finally cold-rolled bases. Similar properties and production stages are also stated in European patent application No. 0,067,632;
better roughening properties and surface topography due to the presence of Sn, In, Ga and/or Zn in the alloy (European patent application No. 0,096,347); and
better roughening properties and surface topography due to the reduction of the Cu content (European patent application No. 0,097,318).
Among the aluminum alloys listed above, in general those having a high Al content of more than 99.0%, in particular of at least 99.5%, are distinguished by good or very good roughening properties but are frequently not sufficiently thermally stable for use in modern procedures for processing printing plates to printing forms, i.e., they exhibit fatigue, for example, as a result of exposure to the high temperatures of more than 180.degree. C., in particular more than 240.degree. C., which are required during baking of positive-working reproduction layers. Although aluminum alloys having a low Al content frequently possess better thermal stability, they are generally inferior in their roughening properties, in particular in the uniformity of the surface topography.
Without any reference to the printing plate art, U.S. Pat. No. 3,989,548 describes aluminum alloy sheets with uniformly distributed intermetallic particles (compounds), the alloy containing at least two elements from the group comprising Fe, Ni, Mn and Si. At least 1.2% of Fe, 1.1% of Ni, 0.3% of Mn and 0.5% of Si must be present in the alloy in each case. The production procedure comprises casting the alloy with a particular growth rate at the solidification front and a particular temperature gradient in the liquid metal in the region of the solidification front. The cast alloy is subsequently subjected to hot and/or cold working with the aim of effecting a cross-sectional reduction of at least 60%. An Al-Fe-Mn alloy preferably has an Fe content of 1.4 to 2.0% and an Mn content of 0.3 to 1.2%, this special alloy furthermore containing Zn, Li, Cu, Mg and Si in a total amount of up to 1.5% and in individual amounts of not more than 1.0% in each case (individual component), as well as other elements, such as Ni, Cr, Co or B in a total amount of up to 1.0% and in individual amounts of not more than 0.3% in each case.